World Trade Center - was building responsible for collapse?

[Richard Haut]

[tenenbaum]

Dear -,
The considerations by Professor Abolhassen Astaneh-Asl, you referred to (http://www.designnews.com/article/CA6363426.html?nid=2332&rid=#reg_visitor_id_2), are inconsistent with the fact that WTC1 was remaining standing almost twice as long as WTC 2 after the impacts. If his theory was true, both the towers should have collapsed after standing for approximately the same periods of time after the impacts by airplanes. In other words, his theory is incomplete at best, a bit too simplistic, and without a significant novelty, but he cut by approx. half the temperature, which the collapse could have occurred at. Bravo, that is the right direction of considerations, but it would be nice, if his considerations included also, what happened to the floors, and not only to the columns and joists!

[Architorture]

[mx2]

What I am trying to say, in the simplest terms, is that it is economically infeasible to build commercial towers (like the Twin Towers) and make them "bullet-proof"....

Bunkers may seem cheap to build but their costs lay in the site work (digging). The added cost is extraordinary and simply would make the real estate to expensive...

It makes more sense to not build any new towers and/or end terrorism.

I expect neither to happen any time soon...unfortunately.

mx2

[expressivestructure]

From what I understand both buildings fell for different reasons. One being the collapse of the center tube, the other having its outer shell pulled inward by the enlarged sagging trusses, creating a domino effect and than a subsequent panacaking of each floor. Both had there fire insulation blown off the during the plane's impact, leaving exposed steel, which consequently heated much quicker and lowered it's yield point. Also the center tube was clad in drywall, which was also destroyed by the planes impact. Both towers were very strong engineered with large amounts of redunadancy - hence the ability to withstand the full speed impact of a 767, a much larger plane than in operation in 1966. The tube design was ingenious for it's day and still is today. The building far exceeded current building codes of the day. If you must find fault in, it would be in the building code of it's day.

[mx2]

I cannot confirm the details but the premise is the same; it's not the impact of a plane that caused any of the towers to collapse, nor was it simply fire. It was the combination of the impact that left the structure vulnerable to an unusually large quantity of spilled fuel that had a hotter and longer burning "effeciency" (higher octane) than what was previously being used in airplanes when it was first designed and built.

In other words, had the two planes been empty of fuel, there would have been no collapse and had the fuel had a lower octane then the heat from the fire would not have lowered the yield strength of the steel so quickly either...perhaps at least allowing for evacuation.

And an added note; a concrete core would not have allowed for such height. The steel tubing was definitely genius for its time (still is really) but it did mean to allow for flexibility and to lessen the total dead load they had to use a fire rated core with gypsum wallboard (probably triple layered/staggered with fire proofing and dampers everywhere)...there are not many alternatives to this, if any. And IF we are to design new towers of the same height (which we don't seem to be for these reasons, I reckon) the problems are the same. To go so high results in a more vulnerable approach...period.

There is no such thing as "fire-proof".

mx2

[P.C.]

"here is no such thing as "fire-proof"."

I do not agrea --- even a paper cup will prove that before the water in it is gone it will burn. A structure of two steel tubes one inside the other , so the wall between them can be filled with a smaller quantity of water will be able to restand huge fires --- as long as the water are still there just the process producing steam from the water, will requier huge amounts of energy.
------- Just ask "how" to manufactor such a framework of hollow square tubework.

[mx2]

This link offers the best (unbiased) explanation in my opinion:

http://en.wikipedia.org/wiki/Collapse_of_the_World_Trade_Center

I was wrong on one major point; the fuel burned off in probably 10 minutes, HOWEVER, it was the penetration of the fuel spill that ignited many large fires simultaneously.

mx2

p.s. there is no such thing as fire PROOF!!! Fire resistant yes!! But everything burns or evaporates at some point...

[Architorture]

[Architorture]

i'm in agreement with mx2, as i stated earlier, building high is inherently dangerous when considering catostrophic events...

most skyscrapers are essecially tightly sealed boxes with a big chimney in the middle and a much more open bottom... not exactly the best recipe for stopping a fire from spreading or growing...

for the most part there has been very little done to remedy these problems throughout the history of the skyscraper...

stairs and elevators are not leasable space so naturally there is an inclination to limit their size and influence on the floor plan...so there is a constant juggling of priorities...

one of the only 'innovations' i can think of in making skyscrapers safer is the bridge in the petronas towers... the observation was made that the most deadly fires in highrises were those that started near the bottom of the building effectively cutting off escape...

jon pickard, designer of the petronas towers and a few WTC neighbors, took account of the bombing of the early 90's WTC and the potential for it to have been much more disasterous...

the bridge in the petronas towers was incorporated at least in part to offer a second means of escape half way up the building in case a fire at the base of one of the buildings elminated the chance of escape...


of course, its rare that skyscrapers come in pairs such as petronas or the WTC... but at least it was a thoughtful solution to a very real problem...

[tenenbaum]

There was not found even the slightest piece of core column indicating any severe physical damage from the airplane impact supporting the NIST’s theory. Without such evidence, the essential role of the hat trusses supporting the allegedly cut core columns and explaining the collapse differences between WTC 1 and 2 is only a wish making the NIST’s theory simply a fairytale described at http://en.wikipedia.org/wiki/Collapse_of_the_World_Trade_Center.

The WTC pieces had fallen down in one spot, and got retrieved all. Torn pieces by the airplane impact would have been very distinctive from any other bent ones, and virtually impossible to miss, but none was found. An Ove Arup’s simulation clearly indicated that only the engine’s shafts had capacity to tear a column, and there were only two of them per airplane in each tower - not enough to cause damage needed for the NIST’s theory to work.

[mx2]

I'm confused...if the trusses and columns did not fail then how did the towers collapse? Or are you saying the impact did not cut enough columns to create the failure? The NIST report agrees with that premise stating that it was really the ensuing fires that added to the weakening of the structure...

mx2

[tenenbaum]

I am saying that no evidence was ever found that any core columns had been cut at all, and only max. 2 core columns could have been cut by only two engine shafts from each airplane, but one engine flew near WTC 2’s core, so only one core column could have been cut at WTC 2, but – ironically – WTC 2 fell down almost twice as fast as WTC 1. In other words, WTC 2 with the core cut (damaged) less than WTC 1’s (one engine flew near WTC 2’s core not damaging it) fell down almost twice as fast as WTC 1 with the more damaged core.

So, damage to core columns from cutting does not support the collapse at all, because less damage could not have caused faster collapse. Almost identical fires at WTC 1 and 2 also do not support that the WTC 2 fell down almost twice as fast as WTC 1. So, a combination of fires and damage to the core columns also does not support the WTC collapse, because neither component of the combination supports it. So, the NIST’s theory is false.

[Richard Haut]

mx

Eugene knows far more about the details than I do, but remember that aircraft are frail structures.

there is very little in an aircraft that has any inherent strength (this was particularly relevant in the Pentagon attack).

had the aircraft been loaded with explosives, OK - but they were not. And the fire in Tower One was very high up.

if anybody needs to scare themselves further without indulging in conspiracy theories, look no further than the FBI's own records on the earlier attack on the basement of the Twin Towers. There is no secret that they had a turned member on the terrorist team - an Egyptian who correctly reported to the FBI what was to happen and suggested that the real explosive be switched for dummy powder and the whole gang arrested. The FBI refused.

"how did the towers collapse" ?

I have no idea - but Eugene has my vote for keeping on looking.

[mx2]

Aaah...now I see my confusion. I need clarification though because I think your point may be moot. The NIST theory supports (no pun intended) the idea that the perimeter columns buckled and lead to the collapse of the towers. I did not see any mention of the core being compromised by the impact...although they did speak of issues related to fire and fire proofing. But you mention the combo of fire and impact could not have lead to its collapse. Obviously I disagree but perhaps I missed it...how then do you propose they collapsed?

mx2